Method and apparatus for making corrugated crown caps

ABSTRACT

A corrugated crown cap shell is formed by drawing a disc blank into a die having grooves arranged according to a desired pattern of corrugation ridges in the shell skirt. The marginal portion of the blank is closely confined between the face of the die and the end face of a hollow punch surrounding the draw punch. The blank is most closely confined around the margin thereof at points along the edge on the lines of the grooves. For this purpose, the punch end face is provided with a series of radial ribs aligning with the die grooves along the die face. The differential restraint thus effected against the margin of the blank induces buckling thereof along and toward the lines of the die grooves to form corrugation ridges corresponding to the pattern defined by the draw die. Clearances and pressure relief are so established as to provide a substantially free draw, obviating ironing, coldpressing or deep-drawing the material.

nited States Patent Frankenberg 51 Oct. 3, 1972 METHOD AND APPARATUS FOR MAKING CORRUGATED CROWN CAPS [72] Inventor: Henry E. Frankenberg, Hinsdale, Ill.

[73] Assignee: Continental Can Company, lnc.,

New York, NY.

[22] Filed: Sept. 17, 1970 [21] Appl. No.: 72,947

[52] 11.8. C1. ..ll3/12l A, l13/l D, 72/348 [51] Int. Cl ..B2ld 51/00, B2ld 22/00 [58] Field of Search ..1 13/1 D, 121 A, 121 AA; 72/347, 348, 350

[56] References Cited UNITED STATES PATENTS 2,475,830 7/0194 Fink ..l13/121 A 3,543,559 12/1970 Hawkins et a1. ..72/348 FOREIGN PATENTS OR APPLICATIONS 409,185 4/1934 Great Britain ..1 13/1 D 61,753 12/1943 Denmark ..113/1 D Primary Examiner-Richard J. Herbst Assistant Examiner-Michael J. Keenan Att0mey-George E. Szekely, Joseph E. Kerwin and William A. Dittmann 57 ABSTRACT A corrugated crown cap shell is formed by drawing a disc blank into a die having grooves arranged according to a desired pattern of corrugation ridges in the shell skirt. The marginal portion of the blank is closely confined between the face of the die and the end face of a hollow punch surrounding the draw punch. The blank is most closely confined around the margin thereof at points along the edge on the lines of the grooves. For this purpose, the punch end face is provided with a series of radial ribs aligning with the die grooves along the die face. The differential restraint thus effected against the margin of the blank induces buckling thereof along and toward the lines of the die grooves to form corrugation ridges corresponding to the pattern defined by the draw die. Clearances and pressure relief are so established as to provide a substantially free draw, obviating ironing, cold-pressing or deep-drawing the material.

4 Claims, 14 Drawing Figures PATENTEDnms 1912 3,695,201

sum 1 [IF 3 INVENTOR HENRY E. FRANKENBERG BY LQ'2" CL.S HKA PMENTEMM m 3.695.201

' SHEET 2 BF 3 Q I FTQLZ BY QM @BM .ATT'Y METHOD AND APPARATUS FOR MAKING CORRUGATED CROWN CAPS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the formation of shells for corrugated crown caps, more particularly draw forming such shells from light-gauge sheet material.

2. The Prior Art characteristically, a crown cap is a shallow cup with a corrugated skirt which flares out to terminate in a generally horizontal flange. The upper part of the skirt is generally cylindrical. The corrugations define ridges beginning just below the top panel, extending along the skirt and terminating in an undulated edge. The corrugations provide stiffening of the skirt requisite for proper crimping, sealing and retention characteristics. The corrugations must be well-formed and uniform. Otherwise, the closure is undependable, particularly under high internal pressures involved with carbonated V beverages.

Crowns for beverage bottles are generally made of soft tin plate or the like. Soft steel plate or strip is inexpensive and easily workable. However, such material is relatively weak and a rather heavy gauge must be used for crowns.

The market for crowns is very large. Extremely low manufacturing costs are manifestly imperative. Correspondingly, automation, suitability of tooling for high production rates and low material cost are very important. Small unit cost savings are highly significant when projected to the large quantities involved.

It has been the practice to form the cap shells by drawforming disc blanks punched from plate, sheet or strip. Completely automated double-acting punch presses are generally used. The tooling consists essentially of a blank-and-form punch and die set. Pressing, ironing, deep-drawing or comparable forming and sizing operations are not usually desirable, since such operations are generally too slow for acceptable manufacturing economy. In usual practice, only a shallow, light draw is involved. Tin-plate or coated tin-free steel of about T-4 temper has been found to provide the requisite physical properties for volume production of crowns having a suitable configuration.

Light-gauge steel is highly susceptible to wrinkling and irregular buckling when drawn to form such articles as crown cap shells. To insure uniform corrugations, the configuration and dimensions of the finished shell have heretofore been selected according to a natural buckling pattern which develops in a free draw. The draw die is then configured substantially to match such 737 natural" corrugation of the material. The tools work the skirt material very lightly, essentially only so much as to limit ovality and warp and to inhibit irregular formation which otherwise may develop due to small variations in thickness and physical properties of the material.

It has been proposed to reduce the cost of crown caps by using somewhat higher temper, lighter gauge material than the 85--95 No. soft steel plate heretofore in general use. For example, 55 No. double-reduced plate having about T-8 temper affords desirable properties and potential savings in material costs. However, such material has not heretofore been found practicable, because it does not produce uniform corruga tions when formed into crowns of popular sizes in accordance with prior manufacturing techniques. Cold pressing, deep drawing, or similar techniques are impractical for reasons above noted. Also, the thinner, harder material is rather prone to cracking, tearing, scuffing and other flawing when heavily worked.

Flaws most often develop in the corrugations, where the material is most severely deformed. Incipient flaws may be exhibited only when crimping the cap on the bottle, resulting in loss of cap, bottle and contents. Coating defects in the corrugated areas may escape detection, in which case unsightly corrosion occurs during storage. Similarly, undetected weak spots may result in creep failure and consequent leakage or spoilage of the contents in shipment or storage. Beer and beverage closures are particularly susceptible to the latter type of failure, because of high internal pressure severely stressing the corrugated cap skirt. Even small loss of carbonation may have a deleterious effect on flavor of the beverage.

SUMMARY OF THE INVENTION The principal object of this invention is to provide a method and tooling for economically producing wellformed corrugated crown cap shells from materials of lighter gauge and higher temper than heretofore feasible.

The foregoing and other objectives are achieved by differentially restricting deformation of the marginal portion of the blank during the draw. Displacement of material in the margin away from the face of the die is restricted more closely at points on the lines of the die grooves than therebetween, by means of a hollow punch having its annular face provided with radial ribs aligned with grooves of the draw die corresponding to the desired corrugation ridges. The same hollow punch may serve as the blanking punch. The flat segments of the punch nose closely restrain the edge of the blank relative to the face of the die between the grooves therein. The ribs more closely so restrain material along the lines of grooves. As the edge of the blank tends to lift from the face of the die, the ribs act as anvils. Constrictive forces cause buckling of the material along the lines of the ribs and into the grooves. The flat portions of the-punch face inhibit buckling, wrinkling or pleating of the blank between the grooves. The desired regular formation of corrugations is thus achieved. Furthermore, scuffing, seizing, and tool breakage are obviated. Tool clearances are so established that there is no substantial impedance of the draw, and thus no ironing, stretching or other heavy working of the material which might result in tearing the material or damaging coating or decoration.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a typical crown cap shell, with prior art tooling shown. in phantom lines;

FIG. 2 is an enlarged fragmentary cross-section showing a portion of the shell as seen in FIG. 1, the section being that through one of the corrugation ridges;

FIG. 3 is an enlarged fragmentary sectional view similar to FIG. 2, but taken diametrically opposite thereto, showing a section in a plane between corrugation ridges;

FIG. 4 is a fragmentary top plan view taken interiorly of the cap shell shown in FIG. 1;

FIG. 5 is a fragmentary bottom plan view taken exteriorly of the shell of FIG. 1;

FIG. 6 is a fragmentary vertical sectional view of a die set according to this invention, the position of the parts being that at completion of the draw, and showing the fully formed shell;

FIG. 7 is a fragmentary top plan view of the draw die shown in FIG. 6;

FIG. 8 is a fragmentary interior elevational view of the draw die shown in FIGS. 6 and 7;

FIG. 9 is a bottom plan view of the hollow punch shown in FIG. 6, showing the series of radial ribs spaced around the end face of the punch;

FIG. 10 is a sectional outline view of the die set of FIG. 6, arranged in a press;

FIGS. 11, 12 and 13 are enlarged fragmentary sectional views of the die set in several stages of the draw; and

FIG. 14 shows the completed shell.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, crown cap shell 10 is the type for which the method and tooling of this invention are primarily intended. Shell 10 has a slightly domed cover panel 11 and a corrugated skirt or flange 12 extending from the panel. The corrugations comprise outwardly projecting ridges 13 extending between the substantially. cylindrical portion 14 of the skirt and the generally horizontal portion 15. The juncture of portions 14 and 15 forms a corner or knuckle 16, adapted for engaging retention means on a bottle finish when the finished cap is crimped thereon.

Representative prior art tooling, shown schematically in phantom lines, comprises a blanking punch 18, blanking die 19, forming punch and draw die 21.

In usual practice, crown cap shells of the type shown are formed from steel. The blanking punch 18 first shears a disc blank from the strip or sheet and moves down to a stop position clear of the blank lying on the face of the die 21. Thereafter the forming punch 20 comes down to draw the blank into die 21, thereby forming the shell 10.

' In order to facilitate use of commercial, soft-temper tin-plate and to form same at extremely high production rates, the tooling is designed for substantially free draw. The tools are configured and sized for liberal clearances and minimal tool pressure on the material. Deformation of the blank occurs along lines of least resistance, particularly with respect to formation of the corrugations. The corrugations are in essence formed in a pattern and configuration which develops by the natural buckling of the material as the marginal portion of blank constricts. The die defines limits on outward deformation of the material and thus inhibits ovality, warping and excessive outward buckling at any one location around the periphery of the blank.

The typical crown corrugation pattern is best seen in FIGS. 2 to 5 inclusive. This pattern is the one found to provide the necessary application and performance characteristics. The number, height, and extent of the ridges are such that the volume of material is accommodated substantially without change in thickness. The configuration is desirably achieved by substantially pure bending deformation. The corresponding stress pattern in such case will reflect a balanced stress distribution, substantially free of sharp gradations or high locked-in stresses. Such forming conditions are generally conducive to regularity of formation notwithstanding commercial variations in thickness and physical properties of the material.

A soft temper material of lighter gauge than that heretofore used does not provide the requisite strength. Any substantial increase in temper is attended by a correspondingly substantial change in draw formation characteristics, particularly with respect to the buckling pattern exhibited in the draw forming operation. Most importantly, higher temper material exhibits a strong tendency toward irregular buckling, aggravated by small variations in thickness and temper. Thus, satisfactory crowns cannot be economically made from material of lighter gauge than that customarily used, according to prior methods and tooling, because of the different corrugation-formation characteristics consequent to the higher temper required.

According to this invention, high quality corrugated crown cap shells can be economically produced from light-gauge high temper material in the configuration above described. Formation of the material is positively controlled so as to induce buckling in the predetermined corrugation pattern without impeding the draw, or imposing high tool pressure on the material.

The method will be best understood in association with the description of the tools according to this invention, with reference to FIGS. 6 to 13.

As seen in FIG. 6, the principal components of the die set are a hollow punch 28, draw punch 30 and draw die 31. Face 32 of die 31 opposes annular face 33 of punch 28. Throat 34 of die 31 is sized to telescope over the nose of punch 30 with a minimum clearance slightly greater than the maximum thickness of the material from which the cap shell 1 10 is formed.

As best seen in FIGS. 7 and 8, face 32 of die 31 is provided with a series of grooves 35 which extend radially along face 32 and axially along the throat 34. Grooves 35 correspond in number, spacing and general contour to the corrugation ridges 113 to be formed in the shell flange. The completed ridges are like those in FIGS. 1 to 5.

Referring now to FIG. 9, face 33 of punch 28 is provided with a circumferential series of radial ribs 37 of the same number as the number of grooves 35 in die 31 and of a cross-section which is generally complementary to that of grooves 35. As seen in FIG. 6, ribs 37 are of uniform height throughout their radial extents. The ribs span an annulus having an inside diameter slightly larger than the inside diameter of punch 28 and an outside diameter slightly smaller than the outside diameter of punch 28. Annular land 29, surrounding the ribs, serves as a position control, as later shown.

Referring again to FIG. 6, the tool parts are arranged with punch 28 so oriented that ribs 37 align with the matching grooves 35 in die 31. The annulus of ribs 35 has an outside diameter slightly less than the initial diameter of blank 40, shown in the broken lines. The position of punch 30 at initiation of the draw is also indicated in broken lines. The solid lines represent the position of the tool parts and the form of the piece part at completion of the draw.

The forming operation is best understood by reference to FIGS. 10 to 13. FIG. 10 is an outline view of a representative set-up in a double-acting punch press, having a first action platen 41, second action ram 42 and a bolster 43. Platen 4l acts on punch 28. In the arrangement shown, punch 28 serves as a blanking punch co-operating with blanking die 46 to shear a disc blank 40 from a sheet when platen 41 descends on the first action of the press, the stroke being limited by die face 32 and the grip pressure limited by cushioning spring 44. As draw punch 30 descends, blank 40 rests on face 32 of die 31. Punch 28 rests on the blank with the crests of ribs 30 upon or very close above the upper face of the blank, the plane of land 29 being flush with or slightly beyond the rib crests. Punch face 33 opposes blank 40 between grooves 35, face 33 lying in a plane set back from the crests of ribs 37. In order to accommodate variation in thickness and flatness of the blank, the die face 32 may be slightly relieved along the lines of grooves 35, minimizing coining or ironing effects. As will be understood in the ensuing description it is the relative positions of the punch face and'ribs thereon in relation to the plane of die face 32 which principally determines the proper formation of the corrugations.

Draw punch 30 is here shown in its approach position. Ram 42 is arranged to force the punch 30 down against blank 40 and into the throat 34 of die 31 on the second action of the press so as to draw the blank into the form of the cap shell 110 (FIG. 6). Cushioning spring 44 is calibrated according to the maximum tolerable grip pressure against the blank which corresponds to substantially free draw conditions. Appropriate adjustment of the bias obviates excessive impedance of the draw by reason of pinching the blank between punches 28, 30 and die 31.

FIGS. 11, '12 and 13 show the relative positions of the tool parts and the piece part in initial, intermediate and completion stages respectively. As seen in FIG. 11, at initiation of the draw, blank 40 is closely restrained entirely around its marginal portion between the annular face of punch 28 and face 32 of die 31. Thus, deformation of the marginal portion of the blank away from face 32 is substantially fully inhibited at points along the edge thereof on lines of the die grooves 35, but the draw is not substantially impeded. Punch face 33 less closely restricts deformation of the segments of the blank between the die grooves. The clearance in those areas is preferably on the order of 0.025 inch, the height of ribs 37 being established accordingly. The margin of the blank is thus more closely restrained against deformation away from the face of the die on lines of the grooves than between them.

As punch 30 draws the blank into the die, the edge of the blank inherently tends to kick away from the die face 32. The close restriction of upward deformation opposite ribs 37 substantially fully inhibits such kicking along the lines of the grooves. Referring particularly to FIG. 11, ribs 37 constitute anvils bearing on the'margin of the blank opposite grooves 35, effecting circumferential bending moments under draw forces acting to kick the edge away from the die face 32 between the grooves. Thus, substantially at the outset of the draw, incipient outwardly projecting ridges are induced in the marginal material of the blank opposite the die grooves. As the draw proceeds, constrictive forces acting on the material in the marginal annulus of the blank radially outward of throat 34 induce buckling of that material to accommodate the volume at reduced mean diameter. Such buckling is pronounced in thin steel stock, which does not readily cold-flow.

Due to the induced predisposition toward outward ridges along the lines of the die grooves, the material buckles outward along those lines of least resistance, an intermediate stage being shown in FIG. 12. As the draw proceeds, the material 213 forming the ridges buckles into the grooves. Groove geometry is established so as to substantially freely accommodate the material along a regular contour, with only such restriction as will inhibit irregular formation which might otherwise be induced by unavoidable variations in the thickness and physical properties of the material. Exact die geometry can best be determined for a particular cap shell and material thereof by means of proving dies, as is understood by those experienced in draw die design. The example here shown involves a shell whose basic size and contour are designedly the same as for ones formerly made of other material. It has been found that substantially the same corrugation die geometry is adaptable, despite differences in draw characteristics of the different materials.

The induced buckling formation of the ridges in grooves 35 relieves constriction stresses in the outer annulus of the blank, obviating wrinkling between the ridges. Face 33 inhibits inward buckling of material along the edge of the blank, restricting displacement of the edge away from the die face at a common plane only slightly above the original plane of the upper face of the blank.

As seen in FIG. 13, upon completion of the draw, flange portion is held generally horizontal. The ridge portions 1 13 are restrained only on the outside by the face of die grooves 35, while the flange portions between the ridges are restrained only from the inside by punch face 33. There is substantially no squeezing or ironing of the material, or risk of tool binding. The contact pressures are merely those relatively light ones incident to inhibiting irregular formation, warping and the like. Thus, the operation can be performed at high speed without high tool pressure and attendant risks of smashing the tools or tearing, scuffing, scraping or overdrawing the material in forming the corrugations.

FIG. 14 shows the resultant cap 110, characterized by substantial freedom from irregular pleating, wrinkles or other deviations from the desired corrugation pattern. Coating and decoration are substantially unblemished and desired crimping characteristics are assured by the well-formed flange.

Because the method and tooling described do not impose severe draw conditions, light gauge material can be used successfully. There is minimal risk of destructive bending, tearing, locked-in stresses, or similar difficulties, such as might otherwise be encountered with light gauge steel of ordinary commercial quality. It is not necessary to resort to material of deep draw quality or other special grades, which entail such cost extras as to be uneconomical for the article here involved. However, the method and tooling of the invention are not limited to use with the preferred material indicated. The invention affords advantages for formation of corrugated crown cap shells from other materials as well, both ferrous and non-ferr0us, in regard to realizing improvements in quality and savings in material and manufacturing costs, as compared with methods and tooling heretofore known.

It will also be understood that variations may be made in the arrangement of the tools from that of the example above given. By way of example, the punches and dies may be inverted from the positions shown, or the die may be mounted on a movable platen, or both, according to the construction of the press or other machine employed, various types being available which may be found well-suited to practice of the invention. Other variations within the spirit and scope of the invention defined in the appended claims will be apparent to those skilled in the art.

What is claimed is:

1. In a method of forming a corrugated crown cap shell from a disc blank, including positioning the blank over the throat of a corrugating die having a circumferential series of grooves on lines extending radially along the face of the die and starting radially inwardly of the periphery of the die, and then drawing the blank into the throat to form the shell, the step comprising closely restricting displacement of material in the marginal portion of the blank in a direction away from the die face at least while initially drawing the blank and radially outwardly of the die grooves constricting the marginal portion thereof with ribs opposing said die and more closely restricting displacement of the material at points along the edge of the blank on the lines of the die grooves than therebetween and inducing buckling of the blank away from the die to form corrugation ridges along and toward the die grooves.

2. In tooling for forming a corrugated crown cap shell from a disc blank, including a draw die having a planar end face and a flared throat with a circumferential series of grooves therein on lines extending radially along the face of the die, said grooves starting radially inwardly of an outer edge of said end face, a cylindrical draw punch, and a hollow cylindrical punch concentric therewith having an annular face adapted to oppose said face of said die during drawing of a blank therein to form a shell, the improvement comprising:

a circumferential series of radial ribs of the same number and spacing as said grooves projecting from said face of said hollow punch, and said ribs extending radially outwardly beyond said grooves and cooperating with said draw die planar end face to induce buckling of the blank away from said die between the lines of said grooves upon closely opposing said punch face to the marginal portion of a blank during drawing thereof in said die.

3. The invention defined in claim 2, said ribs being low and major portions of all segments of said punch face between said ribs lying in a common plane, whereby said hollow punch is adapted to inhibit buckling of the marginal portion of a blank in a direction away from said die face.

4. The invention defined in claim 3, said ribs terminating outwardly on a circle smaller than the outside diameter of said punch face, said punch face and the outside surface of said hollow punch intersecting in a sharp comer defining a circle, whereby said hollow punch is adapted for punching a disc blank from sheet material. 

1. In a method of forming a corrugated crown cap shell from a disc blank, including positioning the blank over the throat of a corrugating die having a circumferential series of grooves on lines extending radially along the face of the die and starting radially inwardly of the periphery of the die, and then drawing the blank into the throat to form the shell, the step comprising closely restricting displacement of material in the marginal portion of the blank in a direction away from the die face at least while initially drawing the blank and radially outwardly of the die grooves constricting the marginal portion thereof with ribs opposing said die and more closely restricting displacement of the material at points along the edge of the blank on the lines of the die grooves than therebetween and inducing buckling of the blank away from the die to form corrugation ridges along and toward the die grooves.
 2. In tooling for forming a corrugated crown cap shell from a disc blank, including a draw die having a planar end face and a flared throat with a circumferential series of grooves therein on lines extending radially along the face of the die, said grooves starting radially inwardly of an outer edge of said end face, a cylindrical draw punch, and a hollow cylindrical punch concentric therewith having an annular face adapted to oppose said face of said die during drawing of a blank therein to form a shell, the improvement comprising: a circumferential series of radial ribs of the same number and spacing as said grooves projecting from said face of said hollow punch, and said ribs extendiNg radially outwardly beyond said grooves and cooperating with said draw die planar end face to induce buckling of the blank away from said die between the lines of said grooves upon closely opposing said punch face to the marginal portion of a blank during drawing thereof in said die.
 3. The invention defined in claim 2, said ribs being low and major portions of all segments of said punch face between said ribs lying in a common plane, whereby said hollow punch is adapted to inhibit buckling of the marginal portion of a blank in a direction away from said die face.
 4. The invention defined in claim 3, said ribs terminating outwardly on a circle smaller than the outside diameter of said punch face, said punch face and the outside surface of said hollow punch intersecting in a sharp corner defining a circle, whereby said hollow punch is adapted for punching a disc blank from sheet material. 